Don't know what that file extension is? You can use Filext.com to find out.

Although we've talked about file extension databases before here at Lifehacker, Filext is worth mentioning because it's just so good. It's a pretty easy program to use; all you have to do is enter the file extension in the Search box, and Filext comes back with a whole ream of good info: function, classification, identifying characters, etc.